Proximity sensor with crosstalk compensation

Abstract

A proximity sensor ( 1 ) with crosstalk compensation comprises a transmitting circuit ( 10 ) to transmit a signal to be reflected at a target ( 2 ) and a disturbing object ( 3 ), and a receiving circuit ( 20 ) to receive a reflected signal (RS) having a useful component (RSI) and a noise component (RS 2 ). The receiving circuit ( 20 ) comprises an output node (A 20 ) to provide an output signal (Vout 2 ) in dependence from the distance of the proximity sensor ( 1 ) from the target ( 2 ). The receiving circuit ( 20 ) comprises a crosstalk compensation circuit ( 100 ) comprising a first charging circuit ( 110 ) to provide a first charge for for coarse crosstalk compensation and a second charging circuit ( 120 ) to provide a second charge for fine crosstalk compensation. A control circuit ( 30 ) sets an amount of the first and the second charge so that the output signal (Vout 2 ) of the crosstalk compensation circuit ( 100 ) is dependent on the useful component (RSI) and independent on the noise component (RS 2 ) of the reflected signal (RS).

The invention claimed is: 
     
       1. A proximity sensor with crosstalk compensation, comprising:
 a transmitting circuit to transmit a signal to be reflected at a target and a disturbing object, 
 a receiving circuit to receive a reflected signal having a useful component and a noise component, the useful component caused by the reflection of the signal at the target, the noise component caused by the reflection of the signal at the disturbing object, the receiving circuit comprising an output node to provide an output signal in dependence on the distance of the proximity sensor from the target, 
 wherein the receiving circuit comprises a detection circuit to detect the reflected signal and an evaluation circuit having an input side to receive the detected reflected signal and an output side to generate the evaluation signal in dependence on the reflected signal, 
 wherein the receiving circuit comprises a signal node to apply the evaluation signal being generated by the evaluation circuit of the receiving circuit in dependence on the reflected signal, 
 wherein the receiving circuit comprises a crosstalk compensation circuit to generate the output signal, the crosstalk compensation circuit being coupled to the signal node, 
 wherein the crosstalk compensation circuit comprises a first charging circuit to provide a first charge and a second charging circuit to provide a second charge, the first and the second charge being applied to the signal node, 
 a control circuit to control the first and the second charging circuit to set an amount of the first and the second charge so that the output signal of the crosstalk compensation circuit is dependent on the useful component and independent on the noise component of the reflected signal. 
 
     
     
       2. The proximity sensor of  claim 1 ,
 wherein the receiving circuit is configured to generate the evaluation signal with a first component being dependent on the useful component of the reflected signal and with a second component being dependent on the noise component of the reflected signal. 
 
     
     
       3. The proximity sensor of  claim 2 ,
 wherein the control circuit controls the first and the second charging circuit such that a sum of the amount of the first and the second charge compensates the second component of the evaluation signal, 
 wherein the crosstalk compensation circuit is configured to generate the output signal dependent on the first component of the evaluation signal and independent on the second component of the evaluation signal. 
 
     
     
       4. The proximity sensor of  claim 1 ,
 wherein the first charging circuit is configured to provide the amount of the first charge being higher than the amount of the charge provide by the second charging circuit. 
 
     
     
       5. The proximity sensor of  claim 1 ,
 wherein the crosstalk compensation circuit comprises an operational amplifier having an input side being coupled to the signal node and an output side being coupled to the output node of the receiving circuit. 
 
     
     
       6. The proximity sensor of  claim 5 ,
 wherein the crosstalk compensation circuit comprises a feedback capacitor being disposed in a feedback path between the output side and the input side of the operational amplifier. 
 
     
     
       7. The proximity sensor of  claim 6 ,
 wherein the crosstalk compensation circuit comprises a first controllable switch being arranged in the feedback path between the feedback capacitor and the input side of the operational amplifier. 
 
     
     
       8. The proximity sensor of  claim 6 ,
 wherein the crosstalk compensation circuit comprises a second controllable switch being arranged in an additional feedback path between the input side and the output side of the operational amplifier. 
 
     
     
       9. The proximity sensor of  claim 1 ,
 wherein the first charging circuit comprises a potentiometer and a storage capacitor, 
 wherein the storage capacitor is charged by the amount of the first charge, the amount of the first charge being dependent from the voltage drop set at the potentiometer. 
 
     
     
       10. The proximity sensor of  claim 9 ,
 wherein the control circuit is configured to set the voltage drop of the potentiometer. 
 
     
     
       11. The proximity sensor of  claim 9 ,
 wherein the storage capacitor has a variable capacitance, 
 wherein the control circuit is configured to set the variable capacitance of the storage capacitor. 
 
     
     
       12. The proximity sensor of  claim 9 ,
 wherein the first charging circuit comprises a controllable switch to couple the storage capacitor of the first charging circuit to the signal node. 
 
     
     
       13. The proximity sensor of  claim 1 ,
 wherein the first charging circuit comprises a controllable current source and a controllable switch to couple the controllable current source to the signal node, 
 wherein the control circuit is configured to control the controllable current source and/or the controllable switch to set the first charge provided to the signal node. 
 
     
     
       14. The proximity sensor of  claim 1 ,
 wherein the second charging circuit is configured as an offset adjustment circuit for the operational amplifier. 
 
     
     
       15. The proximity sensor of  claim 1 ,
 wherein the evaluation circuit comprises an integrator circuit having an input side being coupled to the detection circuit to receive the detected reflected signal, 
 wherein the receiving circuit comprises a controllable switch being disposed between the output side of the integrator circuit and the signal node to provide the evaluation signal to the signal node.